feat: Add initial project structure and dependencies

This commit introduces the foundational elements of the project:
- `.gitignore` file to exclude build artifacts and environment
  variables.
- `Cargo.lock` and `Cargo.toml` defining project dependencies and
  metadata.
- `diesel.toml` for Diesel CLI configuration.
- Initial migration files (`down.sql`, `up.sql`) for database schema
  setup.
- `rustfmt.toml` for code formatting.
- Basic module structure for database, routes, schema, state, and types.
- `src/main.rs` with basic Axum server setup and dotenv loading.
- `src/routes/system_router.rs` for basic API endpoint.
- `src/state.rs` for managing application state and database connection
  pool.
- Type definitions for Subsonic API responses and extensions.

migrations/2026-02-09-205759-0000_init/down.sql

@@ -0,0 +1,4 @@
+-- This file should undo anything in `up.sql`
+-- down.sql (Diesel)
+DROP TABLE IF EXISTS user_music_folders;
+DROP TABLE IF EXISTS users;

migrations/2026-02-09-205759-0000_init/up.sql

@@ -0,0 +1,28 @@
+-- Your SQL goes here
+CREATE TABLE users (
+  id                  INTEGER PRIMARY KEY AUTOINCREMENT,
+  username            TEXT    NOT NULL UNIQUE,
+  password            TEXT    NOT NULL,
+  email               TEXT    NOT NULL UNIQUE,
+
+  ldapAuthenticated   BOOLEAN NOT NULL DEFAULT 0 CHECK (ldapAuthenticated IN (0,1)),
+  adminRole           BOOLEAN NOT NULL DEFAULT 0 CHECK (adminRole IN (0,1)),
+  settingsRole        BOOLEAN NOT NULL DEFAULT 1 CHECK (settingsRole IN (0,1)),
+  streamRole          BOOLEAN NOT NULL DEFAULT 1 CHECK (streamRole IN (0,1)),
+  jukeboxRole         BOOLEAN NOT NULL DEFAULT 0 CHECK (jukeboxRole IN (0,1)),
+  downloadRole        BOOLEAN NOT NULL DEFAULT 0 CHECK (downloadRole IN (0,1)),
+  uploadRole          BOOLEAN NOT NULL DEFAULT 0 CHECK (uploadRole IN (0,1)),
+  playlistRole        BOOLEAN NOT NULL DEFAULT 0 CHECK (playlistRole IN (0,1)),
+  coverArtRole        BOOLEAN NOT NULL DEFAULT 0 CHECK (coverArtRole IN (0,1)),
+  commentRole         BOOLEAN NOT NULL DEFAULT 0 CHECK (commentRole IN (0,1)),
+  podcastRole         BOOLEAN NOT NULL DEFAULT 0 CHECK (podcastRole IN (0,1)),
+  shareRole           BOOLEAN NOT NULL DEFAULT 0 CHECK (shareRole IN (0,1)),
+  videoConversionRole BOOLEAN NOT NULL DEFAULT 0 CHECK (videoConversionRole IN (0,1))
+);
+
+CREATE TABLE user_music_folders (
+  user_id         INTEGER NOT NULL,
+  music_folder_id INTEGER NOT NULL,
+  PRIMARY KEY (user_id, music_folder_id),
+  FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE
+);